Protein kinase CK2 (CK2) is a highly preservative, ubiquitously expressed protein serin/ threonine kinase present in all eukaryotes. CK2 is one of the earliest protein kinases discovered, but the biological role of CK2 is still far from being completely characterized. Unspecific biochemical properties make CK2 a favorite research subject. Such properties are as follows: I) more than 300 substrates have been identified; II) ability to use either ATP or GTP as phosphorus donor; III) implication in the regulation of several important cellular processes such as transcription, growth control, cell cycle regulation, morphogenesis; IV) extraordinary preservation ability in various organisms. The authors characterize subunits of CK2 and localization. Some physiological influence onto flocculation, polarization/polarity, yeast cell division, iron supply are described on the example of yeast casein kinase. Probable influence of CK2 the regulation of riboflavin biosynthesis is considered.